Beyond Auto: ISO

As you may or may not have noticed, your digital camera has a setting that says ISO with a number after it. You probably never really cared what that meant and how it affected your photography…but today you will find out. Simply put, ISO is how sensitive your camera’s film or digital sensor is to light. With that said, let’s dive into ISO a little bit more to find out how it affects each picture you take. If you really want to know how ISO came to be, I’ve included a section on that at the end of this post.

What Is ISO?

As I mentioned already, ISO is the sensitivity of your camera’s sensor to light. The lower the ISO number, the less sensitive to light your sensor is, and the higher the ISO, the more sensitive to light your sensor of film is. The ISO setting on your digital camera directly relates to the speed of film you used to buy if you used a film camera. The main difference is when you use a film camera, you are stuck with one ISO setting at a time until you finish the roll of film. With digital cameras on the other hand, you can take one photo with ISO 100 and the next with ISO 3200 without even thinking about it. This grants us much greater freedom with our digital cameras as we are not stuck at one level of light sensitivity. That is the down and dirty explanation of ISO on your camera. Now I will show you how that affects your photography.

ISO and Noise

ISO and Noise, or Grain, go hand in hand. The higher your ISO setting, the more visible grain will appear in your picture. A sensor delivers a beautiful almost grain-free photograph at the lowest possible ISO setting. When your camera is set to Auto, it will automatically try to use the lowest possible ISO setting to deliver the clearest image. On the same note, when your camera is in Auto, it will generously turn up the ISO in favor of Shutter Speed so your photo isn’t blurry, the result being a noisier photo.

Below is a 100% crop comparison of the left eye on the piggy bank seen at the top of this post taken at all the ISO settings on the Canon 6D. You will notice that the image is cleaner on the left using low ISO settings, but as the ISO increases, so does the noise. Click on the image to see the full size.

Going Beyond Auto – ISO Comparison (Click for Larger Version)

With that said, if you want to Go Beyond Auto with Shutter Speed or Aperture, but still need a little help from your camera, leave ISO on Auto. However, if you want to be creative and ensure that clean, crisp image…or you want a grainy photo, adjust the ISO yourself and take your photography to the next level.

What ISO Setting Should You Use?

There is not a set answer to this question, but there are a few guidelines to use as a starting point. ISO directly affects your Shutter Speed and Aperture settings. In fact these three components make up what is know as the Exposure Triangle because adjusting one means you have to adjust one or both of the others for proper exposure. We have already learned about different ways to use Shutter Speed and Aperture for creative photography and now you will know how ISO comes into play.

If you are outside on a bright sunny day, you will probably be shooting at or around ISO 100 as there is plenty of light to capture your image. You want the sensor to be less sensitive to light so your photo isn’t overexposed and is crisp. However, what if you are taking pictures at your kid’s sporting event and want to stop motion? You don’t want to open your Aperture any more to maintain a good depth of field, or it is already wide open; but when you increase the Shutter Speed the photo is dark…in comes ISO. If you double the sensitivity of your sensor to light by changing to ISO 200, you can double the shutter speed to compensate. If you need an even faster shutter speed, you could even use ISO 400 or 800 depending on your camera. In the noise diagram above, the Aperture remained the same at f/4.0, but the Shutter Speed changed from 1/3 sec all the way to 1/640 sec as the ISO increased.

On the same note, if you are in a darker setting you may want to use a higher ISO such as 1600 or even 3200 depending on your camera and the amount of noise you want in your photo. You might find yourself at a wedding in a dimly lit chapel and flash photography is frowned upon…crank up your ISO. Doing so will allow you to use a faster Shutter Speed and avoid dark and/or blurry photos. Your photos will certainly have more grain in them this way, but at least you didn’t miss the shot.

It Depends On The Camera…and You

Different cameras allow for different ISO ranges, with different levels of noise at each setting. My Canon Rebel XSi has a range of ISO 100-1600, but my Canon 6D (sponsored link) has a range of ISO 100-25600. I can get relatively clear photos at ISO 400 or below on the Rebel, but ISO 1600 or below on the 6D. As cameras continue to evolve, you will find that these numbers will continue to get higher and clearer with time.

Choosing the correct ISO also has everything to do with how you want your final image to look. Do you want grain or do you want it to be crisp? This is a personal preference as well as a situational preference depending on the amount of available light. If you are using a flash you don’t need a high ISO unless your flash isn’t that bright.

The important thing is that you use these ISO settings as a starting point for your photography. They are good guidelines to achieving great quality images, however each lighting and style situation may require adjustments to your ISO. If you want clear, crisp images and have plenty of light, ISO 100-400 is most likely the way to go. But if you want that grainy film-look or you don’t have plenty of light, ISO 800-3200 will help you get your shot.

Now that you have a basic understanding of the three key elements of exposure (Aperture, Shutter Speed, and ISO), Going Beyond Auto shouldn’t be scary to you. So go ahead and take that camera out of Auto and shoot some amazing photos!

More Information Than You Need – A History of ISO

This information is certainly not necessary for understanding how to use ISO in your photography, but you may find it interesting. Technically ISO stands for International Organization for Standardization and really has nothing specifically related to photography. ISO is the organization that develops standards for just about everything you come in contact with. That USB cable that plugs into your computer, your WiFi network, and even the way your clothes are woven together all have ISO certifications. This way when you pick up something in one store, city, or country, it will be the same somewhere else. It is a very good thing to have common standards and that is what the good folks at ISO do.

Back in the days of film, you picked up a roll that had a speed rating of 50, 100, 200, 400, 800, or 1600. That speed rating was known as the ASA film speed. ASA is an American Standard for film sensitivity that was developed by ANSI, or the American National Standards Institute. That was great if you lived in America, but elsewhere they used a German standard called DIN, or Deutsches Institut für Normung (translated to German Institute for Standardization). DIN had a different set of numbers for film sensitivity, specifically 18, 21, 24, 27, 30, and 33. If you were a photographer back then, you probably knew one or both of these standards, but it could get confusing. That is where ISO comes in and made one International Standard for determining the sensitivity of film, specifically with ISO standard 5800:1987 if you care. In this ISO standard, they determined the film speed for photography which later seamlessly translated into digital sensor sensitivity.